The present invention relates to novel compositions and in particular to novel polymers having a high index of refraction and low dispersive power.
In the design and manufacture of lenses and lens systems, it is often desired to use materials for lens fabrication which combine a high index of refraction, n.sub.D, with low dispersive power or high Abbe number.nu. (.nu. equals the reciprocal of the dispersive power). Materials displaying this combination of optical properties can be used to prepare lenses characterized by very low astigmatism and very low chromatic aberration. The barium and lanthanum crown glasses are especially useful in this regard. Certain dense barium crown glasses, for example, combine a relatively high index of refraction of about 1.57 to 1.62 with a relatively high Abbe number of about 58 to 61. Certain lanthanum crown glasses combine an index of refraction of about 1.65 to 1.70 with an Abbe number of about 55 to 59. Thus, these glasses can be used to fabricate lenses of superior optical performance and provide the lens designer with considerable latitude in the design of precision lenses and optical systems.
It is often preferred to use plastic or, more precisely, polymeric materials, rather than glass, as raw materials for lens manufacture. In general, the polymeric materials which are used can be more easily fabricated into lenses, usually by molding techniques, and provide lenses which are lighter and less expensive than similar glass lenses. The conventional polymers used for plastic lens manufacture do not, however, provide combinations of index of refraction and Abbe number values which can be said to compare favorably with the combinations provided by optical glasses, such as the aforementioned barium and lanthanum crown glasses. Polystyrene, for example, which is a commonly used polymer for plastic lens manufacture, combines a relatively high index of refraction of about 1.59 at 20.degree. C. with a relatively low Abbe number of about 31. Polymethylmethacrylate, another commonly used raw material for plastic lens manufacture, combines a relatively high Abbe number of about 57 with a relatively low index of refraction of about 1.49 at 20.degree. C. Other conventional polymers which are used or are candidates for use as raw materials in plastic lens manufacture also do not provide index of refraction and Abbe number combinations which compare favorably with those provided by optical glasses. As a result, plastic lenses fabricated from the conventional polymers are not capable of providing the optical performance provided by lenses fabricated from optical glasses and, accordingly, are subject to design and use limitations.
Thus, there is a continuing need for new polymers which can be used as raw materials in plastic lens manufacture and which provide index of refraction and Abbe number combinations which exceed combinations provided by the conventional polymers.